Carbon particles containing graphite and graphene are used in a wide range of applications ranging from car tire additives, to lubricants, to electronic materials. Some properties that enable their use in such a wide array of applications are high surface areas, and high electrical and thermal conductivities.
Naturally occurring graphene and graphite materials are mined and processed for use in different applications. Naturally occurring graphite and graphene materials contain high concentrations of impurities, and it is difficult and costly to purify naturally occurring graphite and graphene to obtain higher purity materials.
Various crude or refined hydrocarbons (e.g., methane, ethane, propane, etc.) can also be pyrolized or cracked to produce higher-order carbon substances such as graphene and fullerenes, and hydrogen. However, some of the processes used to produce higher-order carbon substances require the use of catalysts, such as metal catalysts, and result in the presence of impurities within the higher-order carbon substances. Furthermore, some processes require the formation of a “seed” or “core” around which the higher-order carbon substances are formed. Additionally, some of these pyrolysis or cracking processes produce particles that are very small (e.g., less than 100 nm in diameter) and are difficult and expensive to collect.
Some examples of higher-order carbon allotropes are shown in FIGS. 1A-1D. FIG. 1A shows a schematic of graphite, where carbon forms multiple layers of a two-dimensional, atomic-scale, hexagonal lattice in which one atom forms each vertex. Graphite is made of single layers of graphene. FIG. 1B shows a schematic of a carbon nanotube, where carbon atoms form a hexagonal lattice that is curved into a cylinder. Carbon nanotubes can also be referred to as cylindrical fullerenes. FIG. 1C shows a schematic of a C60 buckminsterfullerene, where a single layer of a hexagonal lattice of carbon atoms forms a sphere. Other spherical fullerenes exist that contain single layers of hexagonal lattices of carbon atoms, and can contain 60 atoms, 70 atoms, or more than 70 atoms. FIG. 1D shows a schematic of a carbon nano-onion from U.S. Pat. No. 6,599,492, which contains multiple concentric layers of spherical fullerenes.